Polishing apparatus

ABSTRACT

The present invention relates to a polishing apparatus for polishing a workpiece, such as a semiconductor wafer, to a flat mirror finish. The polishing apparatus comprises a polishing table having a polishing surface, and a top ring, and the workpiece is interposed between the polishing table and the top ring and pressed at a predetermined pressure to polish the workpiece. The polishing apparatus comprises at least two dressing units for dressing the polishing surface by being brought into contact with the polishing surface, which is a surface of a polishing cloth.

This application is a divisional of U.S. Ser. No. 11/113,084, filed Apr.25, 2005 now U.S. Pat. No. 7,040,968, which is a divisional of U.S. Ser.No. 09/787,121, filed Mar. 14, 2001, and now U.S. Pat. No. 6,939,208,which is a National Stage of PCT/JP01/00382, filed Jan. 22, 2001.

TECHNICAL FIELD

The present invention relates to a polishing apparatus for polishing aworkpiece, such as a semiconductor wafer, to a flat mirror finish, andmore particularly to a polishing apparatus comprising a dresser fordressing a surface of a polishing cloth attached to an upper surface ofa polishing table.

BACKGROUND ART

As semiconductor devices have become more highly integrated in recentyears, circuit interconnections have become finer and a distance betweenthese circuit interconnections have become smaller. In case ofphotolithography which can form interconnections that are at most 0.5 μmwide, it is required that surfaces on which pattern images are to befocused by a stepper should be as flat as possible because a depth offocus of an optical system is relatively small. A polishing apparatusfor performing chemical mechanical polishing (CMP) has been used forplanarizing a semiconductor wafer.

In a polishing apparatus for polishing and planarizing a surface of asemiconductor wafer on which a device pattern is formed, a non-wovenfabric has heretofore been used as a polishing cloth attached to anupper surface of a polishing table. However, as ICs and LSIs have becomemore highly integrated in recent years, it is required to reducedifferences in levels of a surface, to be polished, of a device patternduring polishing. In order to meet a demand for polishing so as toreduce differences in levels of a surface, to be polished, of a devicepattern, a polishing cloth made of a hard material, e.g., a polishingcloth of foam polyurethane, has been used.

This type of polishing apparatus comprises, as shown in FIG. 21, apolishing table 402 having a polishing cloth (polishing pad) 400attached thereon and constituting a polishing surface, and a top ring404 for holding a substrate W as a workpiece to be polished, such as asemiconductor wafer, in such a manner that a surface to be polishedfaces the polishing cloth 400. A semiconductor wafer W is polished bythis polishing apparatus as follows: The polishing table 402 and the topring 404 are independently rotated, and, while a polishing liquid issupplied from a polishing liquid nozzle 406 provided above the polishingtable 402, the semiconductor wafer W is pressed against the polishingcloth 400 on the polishing table 402 at a predetermined pressure by thetop ring 404. For example, a suspension of fine polishing particles ofsilica or the like in an alkali solution is used as the polishing liquidsupplied from the polishing liquid nozzle 406. Thus, the semiconductorwafer W is polished to a flat mirror finish by a combined effect of achemical polishing effect attained by the alkali and a mechanicalpolishing effect attained by the polishing particles.

When the semiconductor wafer W is brought into contact with thepolishing cloth 400 and the polishing table 402 is rotated to performpolishing, polishing particles or polishing wastes are attached to thepolishing cloth 400, resulting in a change in properties of thepolishing cloth 400 and a deterioration in polishing performance.Therefore, if an identical polishing cloth 400 is repeatedly used forpolishing semiconductor wafers W, problems such as lowered polishingrate and uneven polishing are caused. In order to overcome suchproblems, conditioning called dressing is performed before, after orduring polishing of a semiconductor wafer to regenerate a polishingcloth.

When dressing of a polishing cloth is performed, a dresser 408 isprovided in the polishing apparatus, and polishing cloth 400 is dressedby the dresser 408 at a time of replacement of a semiconductor wafer Wto be polished, for example. Specifically, while a dressing elementattached to a lower surface of the dresser 408 is pressed against thepolishing cloth 400 on the polishing table 402, the polishing table 402and the dresser 408 are independently rotated to remove polishingparticles and polishing wastes attached to a polishing surface of thepolishing cloth and to flatten and dress the polishing surface in itsentirety, whereby the polishing surface is regenerated.

With respect to dressing of a polishing cloth, in accordance withproperties of the polishing cloth, the conventional polishing apparatuscomprises one dresser selected from the group including a contact-typediamond dresser having diamond particles, a contact-type brush dresserhaving a brush, and a non-contact-type dresser for ejecting a fluid jettoward a surface of the polishing cloth to perform dressing.

However, during dressing of a polishing cloth, it has become necessaryto use different dressers, for example, a dresser for thinly shaving asurface of the polishing cloth for initial surface conditioning beforeuse during polishing, and a dresser for removing clogged aggregation ofslurry (polishing liquid) and polishing wastes from the polishing clothduring a polishing process. If the clogged aggregation of the slurry(polishing liquid) or the polishing wastes are not removed from thepolishing cloth, there is a high possibility that polishing particlesand polishing wastes become attached to the polishing cloth todeteriorate a polishing function, or a surface, to be polished, of asemiconductor wafer is scratched, resulting in lowered yield. Therefore,in the conventional polishing apparatus, two or more dressers havingdifferent dressing elements should be replaced as needed. This work istroublesome and disadvantageously lowers throughput of polishedsemiconductor wafers.

Further, in the conventional polishing apparatus, if the top ring unitand the dressing unit are provided adjacent to each other for reasons ofrestriction of a layout, or if a plurality of top ring units and adressing unit are arranged on a single table so as to interfere witheach other, then dressing can be performed only when the top ring doesnot perform polishing and is positioned at a stand-by position. As aresult, polishing cannot be performed during dressing, and hence anumber of semiconductor wafers to be polished per unit time isdecreased.

A thickness of a thin film formed on a surface of a semiconductor wafervaries from position to position in a radial direction of thesemiconductor wafer depending on a film deposition method orcharacteristics of a film deposition apparatus. Specifically, the thinfilm has a film thickness distribution in the radial direction. Further,the film thickness distribution varies depending on a type of filmdeposition method performed or film deposition apparatus used.Specifically, a position and number of portions having a large filmthickness in the radial direction, and difference in thickness betweenthin film portions and thick film portions, vary depending on the typeof film deposition method performed or film deposition apparatus used.

However, with the aforementioned conventional dresser, an entirepolishing surface is uniformly dressed, so that the entire polishingsurface is regenerated to a uniform condition, whereby the entirepolishing surface has uniform polishing performance. Therefore, if anentire area of a semiconductor wafer is uniformly pressed against thepolishing surface after the polishing surface is regenerated by theconventional dresser, then a polishing rate is identical over the entirearea of the semiconductor wafer. Thus, it is impossible to performpolishing in accordance with the above film thickness distribution, andhence a semiconductor substrate is excessively polished at portionshaving a small film thickness and is insufficiently polished at portionshaving a large film thickness.

SUMMARY OF INVENTION

The present invention has been made in view of the above drawbacks. Itis therefore a first object of the present invention to provide apolishing apparatus comprising a dressing unit which can maintain goodpolishing performance of a polishing cloth used for polishing asemiconductor wafer, and thus can enhance yield and productivity ofpolished semiconductor wafers, and to provide a dressing method fordressing the polishing cloth of the polishing apparatus.

In order to attain the first object, according to one aspect of thepresent invention, there is provided a polishing apparatus with apolishing table having a polishing surface and a top ring for pressing aworkpiece at a predetermined pressure while interposing the workpiecebetween the polishing table and the top ring to polish the workpiece,wherein the polishing apparatus includes at least two dressing units fordressing the polishing surface by being brought into contact with asurface of the polishing surface.

According to a preferred aspect of the present invention, dressers inthe at least two dressing units comprise different dressing elements,respectively.

According to another preferred aspect of the present invention, at leastone dressing unit is a dressing unit comprises a dresser having adiameter larger than that of a workpiece to be polished; and at leastone dressing unit is a dressing unit comprises a dresser having adiameter smaller than that of the workpiece to be polished.

According to a further preferred aspect of the present invention, thedressing unit comprising the dresser having a diameter smaller than thatof the workpiece to be polished is swung during dressing.

According to another aspect of the present invention, there is provideda dressing method for dressing a polishing cloth provided in a polishingapparatus. The dressing method includes: initially conditioning thepolishing cloth, before use for polishing, by a dressing unit comprisinga diamond dresser or an SiC dresser; and conditioning the polishingcloth between processes of polishing a workpiece, by a dressing unitcomprising a brush dresser.

According to still another aspect of the present invention, there isprovided a dressing method for dressing a polishing cloth provided in apolishing apparatus. This dressing method includes: initiallyconditioning the polishing cloth, before use for polishing, by adressing unit comprising a diamond dresser or an SiC dresser; andbetween processes of polishing a workpiece, firstly conditioning thepolishing cloth by a dressing unit comprising a diamond dresser or anSiC dresser, and then conditioning the polishing cloth by a dressingunit comprising a brush dresser.

According to a further aspect of the present invention, there isprovided a dressing method for dressing a polishing surface duringpolishing of a workpiece in a polishing apparatus. This dressing methodincludes: dressing the polishing surface while swinging a dressing unitcomprising a dresser having a diameter smaller than a workpiece to bepolished; and after a top ring is withdrawn, dressing the polishingsurface with a dressing unit comprising a dresser having a diameterlarger than the workpiece to be polished.

According to the present invention, there is no need to replace acontact-type diamond dresser having diamond particles and a contact-typebrush dresser having a brush with each other, and a polishing cloth canbe dressed using a suitable combination of dressers.

It is a second object of the present invention to provide a polishingapparatus which can perform polishing in accordance with a thicknessdistribution of a thin film formed on a surface of a workpiece to bepolished, such as a semiconductor wafer, and thus can obtain uniformityof film thickness after polishing the workpiece.

In order to attain the second object of the present invention, there isprovided a polishing apparatus with a polishing table having a polishingsurface and a top ring for pressing a workpiece against the polishingsurface of the polishing table to polish the workpiece, wherein thepolishing apparatus includes a dresser for dressing the polishingsurface of the polishing table. The dresser dresses an area of thepolishing surface used for polishing a predetermined position of asurface of the workpiece in accordance with a film thickness to bepolished at the predetermined position of the surface of the workpiece.

According to another aspect of the present invention, there is provideda polishing apparatus comprising: at least one of a moving mechanism formoving a dresser on a polishing surface of a polishing table, a rotatingmechanism for rotating a dresser, and a pressing mechanism for pressinga dresser against a polishing surface of a polishing table; and acontroller for controlling at least one of a speed of movement of thedresser caused by the moving mechanism, a rotational speed of thedresser caused by the rotating mechanism, and a pressing load of thedresser caused by the pressing mechanism, within an area of thepolishing surface used for polishing a predetermined position of asurface, of a workpiece in accordance with a film thickness to bepolished at the predetermined position of the surface of the workpiece.

According to the present invention, an area to be dressed can be variedas desired within a polishing surface. Therefore, a polishing cloth usedfor polishing an area in which a film thickness to be polished is largeis dressed more than a polishing cloth used for polishing an area inwhich a film thickness to be polished is small. Thus, an area in which afilm thickness to be polished is large can be polished relatively more,and an area in which a film thickness to be polished is small can bepolished relatively less. Consequently, polishing can be properlyperformed in accordance with a profile (film thickness distribution) ofa surface, to be polished, of a workpiece.

According to one preferred aspect of the present invention, a dresserhas a diameter smaller than that of a workpiece to be polished. Further,the dresser dresses a polishing surface during polishing. Furthermore, apolishing apparatus further comprises a cleaning bath for cleaning thedresser.

According to another preferred aspect of the present invention, thepolishing apparatus further comprises a film thickness measuring unitfor measuring a film thickness of a surface, to be polished, of aworkpiece. With this arrangement, an actual profile of the surface, tobe polished, of the workpiece can be obtained by measurement with thefilm thickness measuring unit, and hence polishing can be performed moreproperly in accordance with the actual profile of each of theworkpieces.

According to a further aspect of the present invention, the polishingapparatus further comprises a second dresser for dressing substantiallyan entire area of a polishing surface against which a workpiece to bepolished is pressed. Preferably, the second dresser has a diameterlarger than that of the workpiece to be polished, and the second dresserdresses substantially the entire area of the polishing surface againstwhich the workpiece to be polished is pressed. With this arrangement,protrusions on the polishing surface can selectively be removed toflatten the polishing surface. Specifically, since portions of thepolishing surface which have been dressed more during polishing are wornearlier than other portions, irregularities are generated on a polishedsurface after a polishing operation. However, dressing by the seconddresser can remove only protrusions of the irregularities to flatten thepolishing surface.

Further, according to another aspect of the present invention, when apolishing surface has been locally worn, the second dresser dressessubstantially an entire area of the polishing surface. With thisarrangement, for example, even when the polishing surface has beenlocally worn due to dressing of another dresser, a state of thepolishing surface can be reset by the second dresser, for therebyperforming the subsequent polishing with higher accuracy.

According to a still further aspect of the present invention, there isprovided a polishing apparatus with a polishing table having a polishingsurface and a top ring for pressing a workpiece against the polishingsurface of the polishing table to polish the workpiece, wherein thepolishing apparatus comprises: a dressing unit integrally having a firstdresser for dressing the polishing surface of the polishing table duringpolishing of the workpiece; and a second dresser for dressing thepolishing surface of the polishing table when the workpiece is not beingpolished. With this arrangement, two dressers having different purposescan be integrated, for thereby reducing necessary space for theapparatus.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view showing an entire structure of a polishingapparatus according to a first embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along line II—II of FIG. 1;

FIGS. 3A to 3C are diagrams showing a detailed structure of a dresser ina dressing unit having a diamond dresser, wherein FIG. 3A is a bottomview, FIG. 3B is a cross-sectional view taken along line a—a of FIG. 3A,and FIG. 3C is an enlarged view of portion b in FIG. 3B;

FIGS. 4A and 4B are diagrams showing a detailed structure of a dresserin a dressing unit having a brush dresser, wherein FIG. 4A is a bottomview, and FIG. 4B is a cross-sectional view taken along line b—b of FIG.4A;

FIGS. 5A and 5B are timing charts showing a series of processes ofpolishing and dressing using the polishing apparatus shown in FIG. 1;

FIG. 6 is a plan view showing an entire construction of a polishingapparatus according to a second embodiment of the present invention;

FIG. 7 is a cross-sectional view taken along line VII—VII of FIG. 6;

FIG. 8 is a timing chart showing a series of processes of polishing anddressing using the polishing apparatus shown in FIG. 6;

FIG. 9 is a front view showing a variant of the embodiment shown inFIGS. 6 and 7, in which large and small dressers are provided;

FIG. 10 is a schematic plan view showing a polishing apparatus accordingto a third embodiment of the present invention;

FIG. 11 is a vertical cross-sectional view schematically showing a mainpart of a polishing section in the polishing apparatus according to thethird embodiment of the present invention;

FIG. 12 is a schematic plan view showing a polishing section in thepolishing apparatus shown in FIG. 10, illustrating a state of initialsurface conditioning of a polishing cloth;

FIG. 13 is a schematic plan view showing the polishing section in thepolishing apparatus shown in FIG. 10, illustrating a state of polishingby a top ring;

FIG. 14 is a timing chart showing an example of a series of operationsin the polishing section shown in FIG. 11;

FIG. 15 is a timing chart showing an example of a series of operationsin the polishing section shown in FIG. 11;

FIG. 16 is a timing chart showing an example of a series of operationsin the polishing section shown in FIG. 11;

FIG. 17 is a flow chart showing an example of a series of operations inthe polishing section shown in FIG. 11;

FIG. 18 is a vertical cross-sectional view schematically showing a mainpart of a polishing section in a polishing apparatus according to afourth embodiment of the present invention;

FIG. 19 is a schematic plan view showing a polishing section in thepolishing apparatus according to the fourth embodiment of the presentinvention, illustrating a state of initial surface conditioning of apolishing cloth;

FIG. 20 is a schematic plan view showing the polishing section in thepolishing apparatus according to the fourth embodiment of the presentinvention, illustrating a state of polishing by a top ring; and

FIG. 21 is a schematic cross-sectional view showing a conventionalpolishing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A polishing apparatus according to a first embodiment of the presentinvention will be described below with reference to FIGS. 1 through 5B.FIGS. 1 and 2 show an entire structure of the polishing apparatusaccording to the present invention, wherein FIG. 1 is a plan view, andFIG. 2 is a cross-sectional view taken along line II—II of FIG. 1. Asshown in FIGS. 1 and 2, the polishing apparatus comprises a polishingtable 1 and a top ring unit 4 having a top ring 3 for pressing asemiconductor wafer 2 against the polishing table 1 while holding thesemiconductor wafer 2. The polishing table 1 is coupled to a motor 15and is rotatable about a shaft of the motor 15, as indicated by anarrow. A polishing cloth 5 is attached to an upper surface of thepolishing table 1.

The top ring unit 4 is horizontally swingable so that the top ring 3 canbe positioned at a delivery position above a pusher 16 for deliveringsemiconductor wafer 2, a polishing position on the polishing table 1,and a standby or refuge position. The top ring 3 is coupled to a motor(not shown) and is connected to an elevator cylinder (not shown).Therefore, the top ring 3 is vertically movable and is rotatable about ashaft of the motor, as indicated by arrows, and can press thesemiconductor wafer 2 against the polishing cloth 5 under a desiredpressure. The semiconductor wafer 2 is attracted to a lower end surfaceof the top ring 3 by vacuum suction or the like. A guide ring 6 forpreventing the semiconductor wafer 2 from being removed from the topring 3 is provided on a lower peripheral portion of the top ring 3.Further, a polishing liquid supply nozzle (not shown) is provided abovethe polishing table 1, and a polishing liquid is supplied onto thepolishing cloth 5 on the polishing table 1 from the polishing liquidsupply nozzle.

The polishing apparatus comprises a dressing unit 8 having a diamonddresser 7, and a dressing unit 14 having a brush dresser 11. Both of thedressing unit 8 and the dressing unit 14 are horizontally swingable sothat the dressers 7, 11 can respectively be positioned at a dressingposition on the polishing table 1 and at a standby or refuge position.The dresser 7 is coupled to a motor 17 for rotation and is connected toan elevator cylinder 18. Therefore, the dresser 7 is vertically movableand is rotatable about a shaft of the motor 17, as indicated by arrows.The dresser 111 is also vertically movable and is rotatable about ashaft by the same mechanism as is the dresser 7.

FIGS. 3A through 3C show a detailed structure of the diamond dresser inthe dressing unit 8, wherein FIG. 3A is a bottom view, FIG. 3B is across-sectional view taken along line a-a of FIG. 3A, and FIG. 3C is anenlarged view of a portion b in FIG. 3B.

As shown in FIGS. 3A through 3C, the diamond dresser 7 is in a disk formand comprises a dresser body 9 provided on a peripheral portion of alower surface thereof, and the dresser body 9 has band-shapedprotrusions 9 a having a predetermined circumferential width forelectrodepositing fine particles of diamond. A diamond electrodepositionring 10 formed by electrodepositing fine particles of diamond isprovided on surfaces of the protrusions 9 a. While the polishing table 1and the dresser 7 are rotated and a dressing liquid such as pure waterand, if necessary, a polishing liquid are supplied from a nozzle (notshown) to a central portion of rotating polishing cloth 5, a surface ofthe diamond electrodeposition ring 10 is brought into contact with asurface of the polishing cloth to thinly shave the surface of thepolishing cloth for dressing. The diamond electrodeposition ring 10 hasa structure such that fine particles of diamond are deposited on thesurfaces of the protrusions 9 a, and portions on which diamond isdeposited are plated with nickel, and hence fine particles of diamondare bonded to the surfaces of the protrusions 9 a by nickel plating.

With respect to dimensions of this dresser, for example, a diameter ofthe dresser body 9 is 250 mm, and a plurality of sectoral members (8members in FIG. 3A) having diamond electrodeposited thereon and a widthof 8 mm are arranged on the peripheral portion of the lower surface ofthe dresser body to form a ring. The diameter of the dresser body islarger than a diameter (200 mm) of a semiconductor wafer as a workpieceto be polished, and the dresser body has a margin on an internalcircumferential side and an outer circumferential side in a radialdirection of the table so that a dressed area of the polishing cloth islarger than an area of a polishing surface that is to be used forpolishing the semiconductor wafer. An SiC dresser using a ringcomprising a plurality of SiC sectors may be used instead of the diamonddresser having a diamond electrodeposition ring. In this case, the SiCdresser has the same structure as the dresser shown in FIGS. 3A through3C, and has a number of pyramid-shaped projections disposed on a surfacethereof of several tens of μm.

FIGS. 4A and 4B show a detailed structure of the brush dresser indressing unit 14, wherein FIG. 4A is a bottom view, and FIG. 4B is across-sectional view taken along line b—b of FIG. 4A. The brush dresser11 is in a disk form and comprises a dresser body 13 having a brush 12on an entire area of a lower surface thereof. While the polishing table1 and the dresser 11 are rotated and a dressing liquid such as purewater and, if necessary, a polishing liquid are supplied from a nozzle(not shown) to a central portion of rotating polishing cloth 5, asurface of the brush is brought into contact with a surface of thepolishing cloth for dressing to remove aggregation of slurry (polishingliquid) and polishing wastes from the polishing cloth.

With respect to dimensions of this dresser, for example, a diameter ofthe dresser body is 238 mm, and the dresser body comprises a nylon brushhaving a length of 7 mm, on an entire area of the lower surface thereof.

The diameter of the dresser body is larger than a diameter (200 mm) of asemiconductor wafer as a workpiece to be polished, and the dresser bodyhas a margin on an internal circumferential side and an outercircumferential side in a radial direction of the table so that adressed area of the polishing cloth is larger than an area of thepolishing surface that is to be used for polishing the semiconductorwafer.

FIGS. 5A and 5B are diagrams showing relationships of operation in timeseries with respect to a series of processes of polishing and dressingusing the polishing apparatus having a construction shown in FIG. 1 forprocessing semiconductor wafers.

In an example shown in FIG. 5A, a surface of a polishing cloth is thinlyshaved by the dressing unit 8 having the diamond dresser 7 (see FIG. 1)for performing initial surface conditioning of the polishing clothbefore use for polishing, and then semiconductor wafer 2 is polished bythe top ring 3 (see FIG. 2). In a period between polishing processes,dressing is performed by the dressing unit 14 having the brush dresser11 (see FIG. 1).

In an example shown in FIG. 5B, a surface of a polishing cloth is thinlyshaved by the dressing unit 8 having the diamond dresser 7 forperforming initial surface conditioning of the polishing cloth beforeuse for polishing, and then semiconductor wafer 2 is polished by the topring 3. In a period between polishing processes, two-stage dressing isperformed. Specifically, dressing is first performed by the dressingunit 8 having the diamond dresser 7, and subsequent dressing isperformed by the dressing unit 14 having the brush dresser 11.

As shown in FIGS. 5A and 5B, according to the polishing apparatus of thepresent invention, the surface of the polishing cloth is thinly shavedby the dressing unit 8 having the diamond dresser 7 for performinginitial surface conditioning of the polishing cloth before use forpolishing, and then the semiconductor wafer 2 is polished by the topring 3 (see FIG. 2). In a period between polishing processes, dressingby the dressing unit 8 having the diamond dresser 7 and dressing by thedressing unit 14 having the brush dresser 11 may properly be combined.

According to the present embodiment, a contact-type diamond dresserhaving diamond particles and a contact-type brush dresser having a brushhave been described as dressers for the dressing units 8 and 14.Further, the dressers may be ones selected from the group including theabove dressers and a non-contact-type dresser for ejecting a fluid jettoward a surface of a polishing cloth to dress the polishing cloth.Furthermore, three dressing units or dressers may be provided in thepolishing apparatus. In the present embodiment, pure water is applied asa dressing liquid used in each of the dressing units. In order to attaina chemical dressing effect in addition to mechanical dressing effect, achemical liquid such as an acid, an alkali, or a surface active agentmay also be used. A polishing surface of the polishing table 1 may beconstituted by a polishing cloth or a grinding stone.

As described above, according to the first embodiment of the presentinvention, a contact-type dresser having diamond particles and acontact-type dresser having a brush are provided as dressers used fordressing a surface of a polishing cloth, i.e., at least two dressingunits are provided. This can eliminate a need to replace one dresserwith another dresser, and at least two selected dressers can properly becombined so as to perform optimum dressing of a polishing cloth.

Next, a polishing apparatus according to a second embodiment of thepresent invention will be described below with reference to FIGS. 6 to8.

FIGS. 6 and 7 are diagrams showing a polishing apparatus according tothe second embodiment of the present invention, wherein FIG. 6 is a planview, and FIG. 7 is a cross-sectional view taken along line VII—VII ofFIG. 6. In FIGS. 6 and 7, reference numeral 101 denotes a polishingtable, reference numeral 103 denotes a top ring unit with a top ring102, reference numeral 105 denotes a dressing unit with a dresser 104having a diameter larger than that of a semiconductor wafer 111 as aworkpiece to be polished, and reference numeral 107 denotes a dressingunit with a dresser 106 having a diameter smaller than that of thesemiconductor wafer 111 as the workpiece to be polished. The dresser 106can be reciprocated along a guide rail 108. A pusher 109 for deliveringa semiconductor wafer to the top ring 102 is provided adjacent to thepolishing table 101. Here, the dresser 104 cannot perform a dressingoperation during a polishing process of the semiconductor wafer 111 bythe top ring 102, and the dresser 106 can perform a dressing operationduring a polishing process of the semiconductor wafer 111 by the topring 102. Specifically, an operation range of the dresser 106 does notinterfere with an operation range of the top ring 102. A polishingsurface of the polishing table 101 may be constituted by a polishingcloth or a grinding stone.

In FIGS. 6 and 7, the dressing unit 105 is rotatable so that the dresser104 can be positioned at a dressing position on the polishing table 101and a stand-by position. The dresser 104 is coupled to a motor 115 forrotation and is connected to an elevator cylinder 116. Therefore, thedresser 104 is vertically movable and is rotatable about a shaft of themotor 115, as indicated by arrows. The top ring 102 is coupled to amotor (not shown) for rotation and is connected to an elevator cylinder(not shown). Therefore, the top ring 102 is vertically movable and isrotatable about a shaft of its motor, as indicated by arrows. Thus, thetop ring 102 can press semiconductor wafer 111 against the polishingtable 101 at a desired pressure. Semiconductor wafer 111 as a workpieceto be polished is attracted to a lower end surface of the top ring 102by vacuum suction or the like. A guide ring 112 for preventing thesemiconductor wafer 111 from being removed from the top ring 102 isprovided on a lower peripheral portion of the top ring 102. Further, apolishing liquid supply nozzle (not shown) is provided above thepolishing table 101, and a polishing liquid is supplied onto a polishingcloth 110 on the polishing table 101 from the polishing liquid supplynozzle. In FIG. 7, reference numerals 113 and 114 respectively denotesdiamond electrodeposition rings. That is, both of the dressers 104 and106 are constituted by a diamond dresser. However, a brush dresser maybe used for the dressers 104, 106.

The dressing unit 107 can be reciprocated along the guide rail 108 so asto horizontally slide along the polishing table 101 and to dress apolishing surface for a semiconductor wafer while sliding on a surfaceof the polishing table. The dresser 106 is coupled to a motor 117 forrotation and is connected to an elevator cylinder 118. Therefore, thedresser 106 is vertically movable and is rotatable about a shaft of themotor 117, as indicated by arrows.

FIG. 8 is a diagram showing a relationship of operation in time serieswith respect to a series of processes of polishing and dressing usingthe polishing apparatus having a construction shown in FIG. 6 forprocessing semiconductor wafers. The dressing unit 105 comprisingdiamond dresser 104 having diamond particles and a diameter larger thana workpiece to be polished is used for performing initial surfaceconditioning of the polishing cloth 110 before use for polishing. Aftercompletion of the initial surface conditioning of the polishing cloth,the top ring 102 receives a semiconductor wafer from the pusher (adevice for delivering a wafer) 109, and is moved to a polishing positionon the polishing table 101. Dressing during polishing of semiconductorwafer 111 is performed by the dressing unit 107 comprising diamonddresser 106 having diamond particles and a diameter smaller than thesemiconductor wafer while sliding the dressing unit 107, because thepolishing table 101 is small. After completion of polishing, the topring 102 is swung above the pusher 109, and the polishing cloth 110 isthen dressed by the dressing unit 105 comprising diamond dresser 104having diamond particles and a diameter larger than the polishedsemiconductor wafer. A time for dressing by the dressing unit 107 duringpolishing of semiconductor wafer 111 may be selected as desired.

FIG. 9 is a front view showing a variant of the embodiment shown inFIGS. 6 and 7, in which large and small dressers are provided. In FIG.9, only a small-diameter diamond dresser 106 is shown with omission of alarge-diameter dresser. As shown in FIG. 9, a contact sensor 120 isprovided at a front end of the small-diameter dresser 106, which canpass through a center of polishing table 101 and be moved in a diametricdirection of the polishing table. A profile (surface waviness) ofpolishing cloth 110, which is defined as unevenness in a radialdirection of a polishing surface (upper surface of the polishing cloth110), can be measured with the contact sensor 120 while reciprocatingthe small-diameter dresser 106 along a diameter of the polishing table101. The polishing cloth 110 can locally be dressed by thesmall-diameter diamond dresser 106 so as to correct measured unevennesson the polishing cloth in a radial direction of the polishing table.After the polishing surface is flattened by the small-diameter diamonddresser 106, a large-diameter dresser using a brush instead of thediamond electrodeposition ring 113 shown in FIG. 7 is used to removepolishing wastes and remaining polishing particles from the polishingsurface. Alternatively, the large-diameter dresser may be constituted bythe diamond dresser as shown in FIG. 7 for flattening the polishingsurface, and the small-diameter dresser may be constituted by a brushdresser for removing polishing wastes and remaining polishing particlesfrom the polishing surface. The polishing surface of the polishing table101 may be a polishing cloth or a grinding stone.

FIG. 9 shows a mechanism for reciprocating the dressing unit 107.Specifically, the dressing unit 107 is constructed so that the dressingunit 107 is reciprocated by rotating a ball screw 121 normally orreversely by a motor 122 for a dresser slider. Reference numeral 123denotes a controller for controlling reciprocation of the dressing unit107 and simultaneously controlling a pressing force of the dresser 106.

As described above, according to the second embodiment of the presentinvention, at least one dresser having a diameter smaller than that of aworkpiece to be polished, and at least one dresser having a diameterlarger than that of the workpiece to be polished, are provided. Thus,dressing can be performed by the small-diameter dresser during polishingto increase a number of semiconductor wafers to be polished per unittime. Therefore, application of the present invention to production ofsemiconductor devices can contribute to good production yield andimproved productivity. When one additional small-diameter dresser isprovided, a necessary number of large-diameter dressers can be decreasedto reduce necessary space for the apparatus.

Next, a polishing apparatus according to a third embodiment of thepresent invention will be described below with reference to FIGS. 10through 17.

FIG. 10 is a schematic plan view showing the polishing apparatusaccording to the present embodiment.

As shown in FIG. 10, in the polishing apparatus according to the presentembodiment, a pair of polishing sections 201 a, 201 b are disposed onone side of a space on a floor, which is rectangular as a whole, so asto laterally face each other. A pair of load/unload units for placingthereon cassettes 202 a, 202 b for accommodating semiconductor wafersare disposed on another side of the space. Two transfer robots 204 a,204 b for transferring a semiconductor wafer are disposed on a lineconnecting the polishing sections 201 a, 201 b to the load/unload unitsto constitute a transfer line. One inverter 205 or 206 is disposed oneach side of the transfer line, respectively, and two cleaning units 207a and 208 a, or 207 b and 208 b are disposed with the inverter 205 or206 interposed therebetween.

In the two polishing sections 201 a, 201 b, apparatuses basically havingthe same specifications are disposed symmetrically with respect to thetransfer line. Each of the apparatuses comprises a polishing table 211having a polishing cloth attached to an upper surface thereof, a topring unit 212 for holding a semiconductor wafer, as a workpiece to bepolished, by vacuum suction and pressing the semiconductor wafer againstthe polishing table 211 to polish the semiconductor wafer, a dressingunit 213 for dressing the polishing cloth on the polishing table 211. Apusher 214 for receiving a semiconductor wafer from the top ring unit212 and transferring the semiconductor wafer to the top ring unit 212 isprovided at a transfer line side in each of the polishing sections 201a, 201 b.

The transfer robots 204 a, 204 b have an articulated arm which isbendable and extendable within a horizontal plane and has upper andlower holding portions which are separately used respectively as a dryfinger and a wet finger. Since two robots are used in the presentembodiment, first robot 204 a is basically responsible for a region fromthe inverters 205, 206 to the cassettes 202 a, 202 b, and second robot204 b is basically responsible for a region from the inverters 205, 206to the polishing sections 201 a, 201 b.

The inverters 205,206 turn over semiconductor wafers, and are disposedat a position which the holding portions of the transfer robots 204 a,204 b can reach. In the present embodiment, the two inverters 205,206are separately utilized as a device for handling a dry substrate and adevice for handling a wet substrate, respectively.

Each of the cleaning units 207 a, 207 b, 208 a and 208 b may be of anytype. For example, the cleaning units 207 a, 207 b provided on a side ofthe polishing sections 201 a, 201 b are of a type such that both sidesof a semiconductor wafer are wiped with a roller equipped with a sponge,and the cleaning units 208 a, 208 b provided on a side of the cassettes202 a, 202 b are of a type such that a cleaning liquid is supplied to asemiconductor wafer while holding an edge thereof and rotating the waferwithin a horizontal plane. The latter also has a function as a drier forcentrifugally drying a semiconductor wafer. The cleaning units 207 a,207 b can perform a primary cleaning of a semiconductor wafer, and thecleaning units 208 a, 208 b can perform a secondary cleaning of thesemiconductor wafer after completion of the primary cleaning.

Next, the aforementioned polishing sections will be described below.FIG. 11 is a vertical cross-sectional view schematically showing a mainpart of the polishing section 201 a shown in FIG. 10, and FIGS. 12 and13 are schematic plan views showing the polishing section 201 a shown inFIG. 10. Only the polishing section 201 a will be described below.However, the following description can be also applied to the polishingsection 201 b.

As shown in FIG. 11, a surface of a polishing cloth 210 on polishingtable 211 constitutes a polishing surface which is brought into slidingcontact with a semiconductor wafer W as a workpiece to be polished. Thepolishing table 211 is coupled to a motor (not shown) disposed below thepolishing table 211 via a table shaft 211 a, so that the polishing table211 is rotatable about an axis of the table shaft 211 a.

As shown in FIGS. 11 through 13, a polishing liquid/water supply nozzle215 is disposed above the polishing table 211. A polishing liquid foruse during polishing, and a dressing liquid (e.g., water) for use duringdressing, are supplied from the polishing liquid/water supply nozzle 215onto the polishing cloth 210. The polishing table 211 is surrounded by aframe 217 for recovering polishing liquid and water, and a tub 217 a isprovided at a bottom of the frame.

An atomizer 216 for spraying a liquid composed of a mixture of nitrogengas and pure water or a chemical liquid onto the polishing surface ofthe polishing cloth is disposed above the polishing table 211. Theatomizer 216 comprises a plurality of spray nozzles 216 a connected to anitrogen gas supply source and a liquid supply source. Nitrogen gas fromthe nitrogen gas supply source and pure water or a chemical liquid fromthe liquid supply source are passed through a regulator or air operatorvalve (not shown) to regulate pressure to a predetermined value, and aresupplied to the spray nozzles 216 a in the atomizer 216 in a mixedstate.

A mixture of nitrogen gas and pure water or a chemical liquid is broughtinto a state of {circle around (1)} liquid fine particles, {circlearound (2)} solid fine particles as a result of solidification ofliquid, or {circle around (3)} gas as a result of vaporization of liquid(bringing the mixture to the state of {circle around (1)}, {circlearound (2)}, or {circle around (3)} being called atomization), and, inthis state, the mixture is sprayed through the spray nozzles 216 a inthe atomizer 216 toward the polishing cloth 210. Which state of liquidfine particles, solid fine particles, or gas the mixture is sprayed inis determined, for example, depending on pressure or temperature ofnitrogen gas and/or pure water or a chemical liquid, or a shape of thenozzles. Therefore, the state of the mixture to be sprayed can bevaried, for example, by properly varying pressure or temperature of thenitrogen gas and/or the pure water or a chemical liquid via a regulatoror the like, or by properly varying the shape of the nozzles.

The top ring unit 212 comprises a rotatable spindle 220, a top ring head221 connected to an upper end of the spindle 220, a top ring shaft 222extended downwardly from a free end of the top ring head 221, and asubstantially disk-like top ring 223 connected to a lower end of the topring shaft 222. When the top ring head 221 is swung by rotation of thespindle 220, the top ring 223 is horizontally moved, and thus can bereciprocated between pusher 214 and a polishing position on polishingcloth 210, as indicated by an arrow A in FIG. 10.

Further, the top ring 223 is coupled via the top ring shaft 222 to amotor (not shown) provided within the top ring head 221, and isconnected to an elevator cylinder (not shown), so that the top ring 223is vertically movable and is rotatable about the top ring shaft 222.Semiconductor wafer W as a workpiece to be polished is attracted to andheld on a lower end face of the top ring 223 by vacuum suction or thelike. By these mechanisms, the top ring 223 can rotate and can press thesemiconductor wafer W held on its lower end face against the polishingcloth 210 at a desired pressure.

The dressing unit 213 regenerates a surface of the polishing cloth 210that has been deteriorated as a result of a polishing operation and isdisposed at a position opposite to the top ring unit 212 with respect toa center of the polishing table 211. As shown in FIGS. 11 through 13,the dressing unit 213 according to the present embodiment comprises twointegrated dressers, i.e., a first dresser 239 and a second dresser 233.As described below, the first dresser 239 is used for dressing thepolishing cloth 210 during polishing, and the second dresser 233 is usedfor initial surface conditioning of the polishing cloth 210 before usein for polishing.

The dressing unit 213 comprises a rotatable spindle 230, a dresser head231 connected to an upper end of the spindle 230, a dresser shaft 232extended downwardly from a free end of the dresser head 231, and asubstantially disk-like second dresser 233 connected to a lower end ofthe dresser shaft 232. When the dresser head 231 is swung by rotation ofthe spindle 230, the second dresser 233 is horizontally moved, and thuscan be reciprocated between a dressing position on the polishing cloth210 and a stand-by position located outside of the polishing table 211,as indicated by arrow B in FIGS. 10 and 12. Further, the second dresser233 is coupled via the dresser shaft 232 to a motor (not shown) providedwithin the dresser head 231, and is connected to an elevator cylinder(not shown), so that the second dresser 233 is vertically movable and isrotatable about the dresser shaft 232. A dresser cleaning bath 218 forcleaning the second dresser 233 is disposed at the stand-by positionlocated outside of the polishing table 211.

Here, the second dresser 233 comprises a diamond dresser 234 of a pelletor ring type as a dressing element. A plurality of disk-like memberswith particles such as diamond particles electrodeposited thereon arearranged on a periphery of a lower surface of the second dresser 233 toconstitute the diamond dresser 234. A diameter of the second dresser 233is, for example, 270 mm, which is larger than a diameter (200 mm) ofsemiconductor wafer W as a workpiece to be polished. Therefore, an areaof the polishing surface which is to be dressed by the second dresser233 is larger than an area of the polishing surface which is to be usedfor polishing the semiconductor wafer W.

A support section 235 is fixed to a lateral portion of the dresser head231, and a swinging motor 236 is fixed to a front end of the supportsection 235. A swing arm 237 is connected to a motor shaft 236 a of theswinging motor 236. The swing arm 237 is swung by rotation of theswinging motor 236. This swinging motor 236 is connected to a controller250 for controlling a speed of the motor (swing speed). The swingingmotor 236 constitutes a moving mechanism for moving the first dresser239, described below, on the polishing surface of the polishing table211.

The dresser shaft 238 is extended downwardly from a free end side of theswing arm 237, and substantially disk-like first dresser 239 isconnected to a lower end of the dresser shaft 238. When the swing arm237 is swung by actuating the swinging motor 236, the first dresser 239is horizontally moved, so that the first dresser 239 can be reciprocatedbetween a dressing position on the polishing cloth 210 and a stand-byposition located outside of the polishing table 211, as indicated byarrow C in FIG. 13. A support base 246 is fixed below the dresser head231 of the spindle 230, and a tub-like dresser cleaning bath 247 forcleaning the first dresser 239 is provided in the support base 246 atthe stand-by position of the first dresser 239. The support base 246 isswung integrally with the dresser head 231 by rotation of the spindle230.

The dresser shaft 238 is connected to an air cylinder (pressingmechanism) 240 fixed to the swing arm 237, and is vertically movable bythe air cylinder 240. Further, the dresser shaft 238 is connected to arotating cylinder 241 via a key (not shown). This rotating cylinder 241has a timing pulley 242 on its periphery. A rotating motor (rotatingmechanism) 243 is fixed to the swing arm 237, and the timing pulley 242is connected via a timing belt 244 to a timing pulley 245 provided onthe rotating motor 243. Therefore, the rotating cylinder 241 and thedresser shaft 238 are integrally rotated via the timing pulley 245, thetiming belt 244, and the timing pulley 242 by driving the rotating motor243, so that the first dresser 239 is rotated.

Here, the first dresser 239 has a disk-type diamond dresser 248 as adressing element. A disk-like member with particles such as diamondparticles electrodeposited thereon is provided on an entire area of alower surface of the first dresser 239 to constitute the diamond dresser248. A diameter of the first dresser 239 is, for example, 100 mm, whichis smaller than a diameter (200 mm) of semiconductor wafer W as aworkpiece to be polished. Therefore, an area of the polishing surfacewhich is to be dressed by the first dresser 239 is smaller than an areaof the polishing surface which is to be used for polishing thesemiconductor wafer W

Thus, the dressing unit according to the present embodiment has aconstruction such that two dressers for different purposes, and acleaning bath for one of the dressers, have been integrated with oneanother. This construction can reduce necessary space for the polishingapparatus.

Next, an operation of polishing semiconductor wafers, and dressing, bythe polishing apparatus thus constructed will be described below. FIGS.14 through 16 are timing charts showing a series of operations in thepresent embodiment.

An example shown in FIG. 14 will be described below.

First, initial surface conditioning of a polishing cloth is performedprior to performing a polishing operation. A surface of the polishingcloth 210 is thinly shaved by the second dresser 233 of the dressingunit 213 for performing the initial surface conditioning of thepolishing cloth before polishing. FIG. 12 shows this state. In thiscase, the dresser head 231 is moved onto the polishing cloth 210 at adressing position by rotation of the spindle 230. Thereafter, the seconddresser 233 and the polishing table 211 are independently rotated, andthe diamond dresser 234 held on the second dresser 233 is brought intoabutment with the polishing cloth 210 under a predetermined pressure. Atthis time, a moment or so before the diamond dresser 234 is brought intocontact with the polishing cloth 210, water is supplied from thepolishing liquid/water supply nozzle 215 onto the upper surface of thepolishing cloth 210 to wash away used polishing liquid remaining on thepolishing cloth 210. Thus, the second dresser 233 can regenerate anentire polishing surface of the polishing cloth 210.

Next, dressing before polishing is performed by the second dresser 233.During, before, or after dressing by the second dresser 233, nitrogengas and pure water or a chemical liquid are supplied to the atomizer 216under a predetermined pressure and temperature, and a mixed liquidcomposed of the pure water or the chemical liquid and the nitrogen gasis sprayed from the spray nozzles 216 a in the atomizer 216 toward thepolishing cloth 210. Thus, the mixed liquid is sprayed in an atomizedstate on the polishing cloth 210, whereby a polishing liquid andpolishing wastes remaining on the polishing cloth 210 are scatteredtoward an outer portion of the polishing table 211. In particular,polishing liquid and polishing wastes that have fallen into recesses inthe polishing cloth can be blown away from the recesses by gas containedin the mixed liquid, and, further, can be washed away by pure water orchemical liquid. Thus, polishing liquid and polishing wastes, whichremain on the polishing cloth 210 to cause a scratch, can be effectivelyremoved. This atomization can be performed at any time during dressingby the second dresser 233, or at any time before or after dressing bythe second dresser 233. Incidentally, as indicated by a dashed line inFIGS. 14 through 16, atomization may also be performed at a time ofinitial surface conditioning of the polishing cloth before polishing.

Water supplied from the polishing liquid/water supply nozzle to thepolishing cloth 210 and the mixed liquid sprayed from the atomizer 216onto the polishing cloth 210 are scattered to an outer portion of thepolishing table 211 by centrifugal force produced by rotation of thepolishing table 211, and are recovered in the tub 217 a provided at thelower part of the frame 217. After completion of dressing, the seconddresser 233 is returned to the stand-by position by swinging the dresserhead 231, and then the second dresser is cleaned in the dresser cleaningbath 218 provided in this stand-by position.

A polishing process of a semiconductor wafer is then performed. Duringpolishing of the semiconductor wafer, not only polishing ofsemiconductor wafer W by the top ring 223 but also dressing by the firstdresser 239 in the dressing unit 213 is performed. FIG. 13 shows thisstate. In this case, the spindle 220 is rotated to move the top ringhead 221 onto the polishing cloth 210 in a polishing position.Thereafter, the top ring 223 and the polishing table 211 areindependently rotated, and the semiconductor wafer W held on the topring 223 and the polishing table 211 are relatively moved to press thesemiconductor wafer W held on a lower surface of the top ring 223against the polishing cloth 210 on the polishing table 211. At thistime, a polishing liquid is supplied from the polishing liquid/watersupply nozzle 215 onto the upper surface of the polishing cloth 210. Forexample, a suspension of fine polishing particles in an alkali solutionmay be used. In this case, the semiconductor wafer W is polished by acombined effect of a chemical polishing effect attained by the alkaliand a mechanical polishing effect attained by the polishing particles.Polishing liquid used for the polishing is scattered to an outer portionof the polishing table 211 by centrifugal force produced by rotation ofthe polishing table 211, and is recovered in tub 217 a provided at thelower part of the frame 217.

During such polishing, the swinging motor 236 fixed to the supportsection 235 in the dressing unit 213 is actuated to swing the swing arm237, thereby moving the first dresser 239 housed in the dresser cleaningbath 247 in the support base 246 onto the polishing cloth 210. The firstdresser 239 is then rotated by the rotating motor 243 to bring thediamond dresser 248 held on the first dresser into abutment with thepolishing cloth 210 under a predetermined pressure for dressing thepolishing cloth 210.

During this dressing, the swing arm 237 and the first dresser 239 areswung by the swinging motor 236. The controller 250 controls motor speedof the swinging motor 236 so that a swing speed of the first dresser 239varies depending on a position of the first dresser 239 on the polishingtable 211. Swing speed of the first dresser 239 is controlled based on aprofile of a surface, to be polished, of semiconductor W. That is, swingspeed is controlled so as to be low at a position of the polishing cloth210 for polishing an area in which a film thickness to be polished islarge, and so as to be high at a position of the polishing cloth 210 forpolishing an area in which a film thickness to be polished is small.Therefore, a polishing cloth used for polishing an area in which a filmthickness to be polished is large is dressed more than a polishing clothused for polishing an area in which a film thickness to be polished issmall. Thus, in the top ring 223, an area in which a film thickness tobe polished is large can be polished relatively more, and an area inwhich a film thickness to be polished is small can be polishedrelatively less. Consequently, this can eliminate excessive polishing orinsufficient polishing. A dressing time of the first dresser 239 duringpolishing of semiconductor wafer W may be selected as desired. Thecontroller 250 in the present embodiment controls swing speed of thefirst dresser 239. Alternatively, in order to eliminate excessivepolishing or insufficient polishing, the rotating motor (rotatingmechanism) 243 or the air cylinder (pressing mechanism) 240 may becontrolled to control a rotational speed or a pressing load of the firstdresser 239.

In another example shown in FIG. 15, initial surface conditioning of apolishing cloth before polishing is performed by the first dresser 239instead of the second dresser 233, and other features in this exampleare the same as the example shown in FIG. 14. Thus, the first dresser239 can be used for initial surface conditioning. In still anotherexample shown in FIG. 16, the second dresser 233 is used only at a timeof replacement of polishing cloth 210, and subsequent dressing isperformed by the first dresser 239. Since a polishing cloth 210 beforeuse is not dressed at all, an amount of time necessary for dressing at atime of initial surface conditioning is long. On the other hand, in acase of a polishing cloth 210 that has been dressed once, polishingefficiency can be increased simply by dressing in a short amount oftime. Therefore, in the example shown in FIG. 16, initial surfaceconditioning is performed in a short amount of time by a large-diametersecond dresser 233, and dressing of portions necessary to be dressed inthe polishing cloth is performed by a small-diameter first dresser 239.This dressing method is suitable for use in a case where dressing cannotbe performed during polishing because of reasons based on a polishingprocess being performed, such as combination of a workpiece to bepolished with a used polishing liquid.

As described above, in the polishing apparatus according to the presentinvention, since the first dresser 239 having a diameter smaller thansemiconductor wafer W, as the workpiece to be polished, is used, an areato be dressed can be varied as desired within a polishing surface. Thus,an amount of dressing can be adjusted at a desired position of thepolishing surface. Therefore, polishing can be properly performed inaccordance with a profile (film thickness distribution) of a surface, tobe polished, of semiconductor wafer W.

Here, for example, distribution of film thickness to be polished onsemiconductor wafer W, that is, a profile of a surface, to be polished,of the semiconductor wafer W, may be previously assumed based on a filmdeposition method or a film deposition apparatus, and at least one ofswing speed, rotational speed, and pressing load of the first dresser239 may be controlled according to a program based on this profile.Further, as shown in FIGS. 11 through 13, a film thickness measuringunit 300 for measuring a profile of a surface, to be polished, ofsemiconductor wafer W before or during polishing may be provided, and atleast one of swing speed, rotational speed, and pressing load of thefirst dresser 239 may be controlled for each of semiconductor wafersbased on an actual profile of a surface, to be polished, ofsemiconductor wafer W, which is measured by the film thickness measuringunit. Thus, when the film thickness measuring unit 300 has beenprovided, polishing can be performed more properly for each of pluralsemiconductor wafers. When a profile of a surface, to be polished, ofsemiconductor wafer W is measured by the film thickness measuring unit300, a pad profiler for measuring a profile of the polishing surface ofthe polishing cloth 210 may additionally be provided to measure theprofile of the polishing surface, and at least one of swing speed,rotational speed, and pressing load of the first dresser 239 may becontrolled based on both of the profile of the surface, to be polished,of the semiconductor wafer W and the profile of the polishing surface ofthe polishing cloth 210.

Further, dressing of the polishing cloth 210 may be performed accordingto a flow chart as shown in FIG. 17. That is, after initial surfaceconditioning is performed by the second dresser 233, the polishing cloth210 is dressed by the first dresser 239, and then a semiconductor waferW is polished. After polishing of the semiconductor wafer W, it isdecided whether or not polishing performance of the polishing cloth 210is properly maintained.

When polishing performance is not properly maintained, a polishingsurface of the polishing cloth 210 in its entirety is dressed by thelarge-diameter second dresser 233. In order to decide whether or notpolishing performance is properly maintained, a profile of a surface, tobe polished, of semiconductor wafer W is measured with the filmthickness measuring unit 300, and it is decided whether or not measuredprofile meets a predetermined level requirement. Thus, in a case wherethe polishing surface has been locally worn, substantially an entirearea of the polishing surface is dressed by the large-diameter seconddresser 233, and hence, even when the polishing cloth 210 has beenlocally worn due to dressing of the first dresser 239, a state of thepolishing cloth 210 can be reset by the second dresser 233.

Next, a polishing apparatus according to a fourth embodiment of thepresent invention will be described below with reference to FIGS. 18through 20. Like parts and components in the present embodiment aredesignated by the same reference numerals as those shown in the thirdembodiment. Parts not particularly referred to in the followingdescription are the same as parts in the third embodiment.

FIG. 18 is a vertical cross-sectional view schematically showing a mainpart of a polishing section in the polishing apparatus according to thepresent embodiment of the present invention, and FIGS. 19 and 20 areschematic plan views showing the polishing section in the polishingapparatus according to the present embodiment of the present invention.

As shown in FIGS. 18 through 20, the polishing apparatus according tothe present embodiment separately comprises a first dressing unit 252having a first dresser 273 for dressing a polishing cloth during apolishing operation, and a second dressing unit 251 having a seconddresser 263 for initial surface conditioning of the polishing clothbefore use during polishing.

The first dressing unit 252 comprises a horizontally extended ball screw270, a dresser shaft 272 extended downwardly from a nut 271 provided onthe ball screw 270, and a substantially disk-like first dresser 273connected to a lower end of the dresser shaft 272. A ball screw drivemotor 274 is connected to one end of the ball screw 270. The ball screw270 is rotated by actuating the ball screw drive motor 274, and the nut271 provided on the ball screw 270, and the first dresser 273 connectedto the nut 271, are horizontally moved via action of the ball screw 270.Thus, the first dresser 273 can be reciprocated between a dressingposition on polishing cloth 210 and a stand-by position located outsideof polishing table 211, as indicated by an arrow E in FIG. 20. This ballscrew drive motor 274 is connected to a controller 280 for controllingspeed of the motor (swing speed). The ball screw drive motor 274constitutes a moving mechanism for moving the first dresser 273 alongthe polishing table 211.

Further, the first dresser 273 is coupled to a rotating motor (rotatingmechanism) 275 fixed to the nut 271 of the ball screw 270 via thedresser shaft 272, and is connected to an air cylinder (a pressingmechanism) 276 via the dresser shaft 272. Therefore, the first dresseris vertically movable and is rotatable about the dresser shaft 272. Adresser cleaning bath 277 for cleaning the first dresser 273 is disposedin the stand-by position located outside of the polishing table 211.

Here, as with the third embodiment, the first dresser 273 comprises adisk-type diamond dresser 278 as a dressing element. A diameter of thefirst dresser 273 is smaller than that of a semiconductor wafer W as aworkpiece to be polished. Therefore, an area of a polishing clothdressed by the first dresser 273 is smaller than an area of a polishingsurface that is to be used for polishing the semiconductor wafer W.

The second dressing unit 251 comprises a rotatable spindle 260, adresser head 261 connected to an upper end of the spindle 260, a dressershaft 262 extended downwardly from a free end of the dresser head 261,and a substantially disk-like second dresser 263 connected to a lowerend of the dresser shaft 262. When the dresser head 261 is swung byrotation of the spindle 260, the second dresser 263 is horizontallymoved and thus can be reciprocated between a dressing position on thepolishing cloth 210 and a stand-by position located outside of thepolishing table 211, as indicated by an arrow D in FIG. 19. Further, thesecond dresser 263 is coupled via the dresser shaft 262 to a motor (notshown) provided within the dresser head 261, and is connected to anelevator cylinder (not shown), so that the second dresser 263 isvertically movable and is rotatable about the dresser shaft 262.

Here, as with the third embodiment, the second dresser 263 comprises apellet-type diamond dresser 264 as a dressing element. A diameter of thesecond dresser 263 is larger than that of semiconductor wafer W as aworkpiece to be polished. Therefore, an area of a polishing clothdressed by the second dresser 263 is larger than an area of a polishingsurface that is to be used for polishing the semiconductor wafer W.

Next, an operation of polishing semiconductor wafers and dressing apolishing cloth by the polishing apparatus thus constructed will bedescribed below. Only operation corresponding to the example, of thethird embodiment, shown in FIG. 14 will be described. However, it isneedless to say that the following description can be applied tooperation corresponding to the examples shown in FIGS. 15 through 17.

First, initial surface conditioning of a polishing cloth prior toperforming a polishing operation will be described. A surface ofpolishing cloth 210 is thinly shaved by the second dresser 263 in thesecond dressing unit 251 for initial surface conditioning of thepolishing cloth before polishing. FIG. 19 shows this state. In thiscase, the dresser head 261 is moved to a dressing position on thepolishing cloth 210 by rotation of the spindle 260. Thereafter, thesecond dresser 263 and the polishing table 211 are independentlyrotated, and the diamond dresser 264 held on the second dresser 263 isbrought into abutment with the polishing cloth 210 under a predeterminedpressure. Thus, the second dresser 263 can regenerate an entirepolishing surface of the polishing cloth 210. After completion ofdressing, the second dresser 263 is returned to a stand-by position byswinging the dresser head 261, and then the second dressser is cleanedin the dresser cleaning bath 218 provided in this stand-by position.

Next, polishing of a semiconductor wafer is performed. During polishingof a semiconductor wafer, not only polishing of a semiconductor wafer Wby the top ring 223, but also dressing by the first dresser 273 in thefirst dressing unit 252, is performed. FIG. 20 shows this state. In thiscase, the spindle 220 is rotated to move the top ring head 221 above thepolishing cloth 210 in a polishing position. Thereafter, the top ring223 and the polishing table 211 are independently rotated, and thesemiconductor wafer W held on the top ring 223 and the polishing table211 are relatively moved to press the semiconductor wafer W held on alower surface of the top ring 223 against the polishing cloth 210 on thepolishing table 211. At this time, a polishing liquid is supplied fromthe polishing liquid/water supply nozzle 215 onto an upper surface ofthe polishing cloth 210, for thereby polishing the semiconductor waferW.

During such polishing, the ball screw drive motor 274 in the firstdressing unit 252 is actuated to move the first dresser 273, housed inthe dresser cleaning bath 277, onto the polishing cloth 210. The firstdresser 273 is then rotated by the rotating motor 275 to bring thediamond dresser 278 held on the first dresser 273 into abutment with thepolishing cloth 210 under a predetermined pressure for dressing thepolishing cloth 210.

During this dressing, the first dresser 273 is moved along the polishingtable 211 in a radial direction of the table 211 by the ball screw drivemotor 274. The controller 280 controls motor speed of the ball screwdrive motor 274 so that swing speed of the first dresser 273 variesdepending on a position of the first dresser 273 above the polishingtable 211. Swing speed of the first dresser 273 is controlled based on aprofile of a surface, to be polished, of the semiconductor wafer W. Thatis, swing speed is controlled so as to be low at a position of thepolishing cloth 210 for polishing an area in which a film thickness tobe polished is large, and so as to be high at a position of thepolishing cloth 210 for polishing an area in which a film thickness tobe polished is small. Therefore, a polishing cloth used for polishing anarea in which a film thickness to be polished is large is dressed morethan a polishing cloth used for polishing an area in which a filmthickness to be polished is small. Thus, in the top ring 223, an area inwhich a film thickness to be polished is large can be polishedrelatively more, and an area in which a film thickness to be polished issmall can be polished relatively less. Consequently, this can eliminateexcessive polishing or insufficient polishing. A dressing time of thefirst dresser 273 during polishing of the semiconductor wafer W may beselected as desired. The controller 250 in the present embodimentcontrols swing speed of the first dresser 273. Alternatively, in orderto eliminate excessive polishing or insufficient polishing, the rotatingmotor (rotating mechanism) 275 or the air cylinder (pressing mechanism)276 may be controlled to control rotational speed or pressing load ofthe first dresser 273.

As described above, in the polishing apparatus according to the presentinvention, since the first dresser 273 having a diameter smaller thanthat of semiconductor wafer W as the workpiece to be polished is used,an area to be dressed can be varied as desired within a polishingsurface. Thus, an amount of dressing can be adjusted at a desiredposition of the polishing surface. Therefore, polishing can be properlyperformed in accordance with a profile (film thickness distribution) ofa surface, to be polished, of semiconductor wafer W.

As with the third embodiment, in the present embodiment, for example, aprofile of a surface, to be polished, of semiconductor wafer W may bepreviously assumed based on a film deposition method or a filmdeposition apparatus, and at least one of swing speed, rotational speed,and pressing load of the first dresser 273 may be controlled accordingto a program based on this profile. Alternatively, a film thicknessmeasuring unit for measuring a profile of a surface, to be polished, ofsemiconductor wafer W before polishing may be provided, and at least oneof swing speed, rotational speed, and pressing load of the first dresser273 may be controlled for each of plural semiconductor wafers based onan actual profile of a surface, to be polished, of semiconductor waferW, which is measured by the film thickness measuring unit.

In the third and fourth embodiments, a diamond dresser is used as thedressing element in both of the second dresser and the first dresser.However, the dressing element is not limited to a diamond dresser. Forexample, not only pellet-type or disk-type diamond dressers but alsoring-type diamond dressers may be used. Further, brush dressers may alsobe used. It is also possible to use a proper combination of thesevarious dressing elements.

As described above, according to the third and fourth embodiments of thepresent invention, since a dresser having a diameter smaller than thatof a workpiece to be polished is used, an area to be dressed can bevaried as desired within a polishing surface. Therefore, a polishingcloth used for polishing an area in which a film thickness to bepolished is large is dressed more than a polishing cloth used forpolishing an area in which a film thickness to be polished is small.Thus, an area in which a film thickness to be polished is large can bepolished relatively more, and an area in which a film thickness to bepolished is small can be polished relatively less. Consequently,polishing can be properly performed in accordance with a profile (filmthickness distribution) of a surface, to be polished, of a workpiece.

It is needless to say that the present invention is not limited to theabove-described embodiments and may be practiced in various differentforms without departing from the scope of the technical idea.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a dresser for dressing asurface of a polishing cloth attached to an upper surface of a polishingtable in a polishing apparatus for polishing a workpiece such as asemiconductor wafer to a flat mirror finish.

1. A method comprising: dressing a polishing cloth by using a firstdresser; polishing a surface of a workpiece by pressing said workpieceagainst said polishing cloth; determining whether or not a polishingperformance of said polishing cloth is properly maintained by (i)measuring a profile of said surface of said workpiece, and (ii)determining whether or not said profile of said surface of saidworkpiece meets a predetermined level requirement; and dressing saidpolishing cloth by using a second dresser when it is determined thatsaid polishing performance of said polishing cloth is not properlymaintained.
 2. A method comprising: dressing a polishing cloth by usinga first dresser; polishing a surface of a workpiece by pressing saidworkpiece against said polishing cloth; determining whether or not apolishing performance of said polishing cloth is properly maintained;dressing said polishing cloth by using a second dresser when it isdetermined that said polishing performance of said polishing cloth isnot properly maintained; and repeating dressing of said polishing clothby using said first dresser and polishing of said surface of saidworkpiece by pressing said workpiece against said polishing cloth whenit is determined that said polishing performance of said polishing clothis properly maintained.
 3. A method comprising: dressing a polishingcloth by using a first dresser; polishing a surface of a workpiece bypressing said workpiece against said polishing cloth; repeating dressingof said polishing cloth by using said first dresser and polishing ofsaid surface of said workpiece by pressing said workpiece against saidpolishing cloth; determining whether or not a predetermined number ofworkpieces has been polished; determining whether or not a polishingperformance of said polishing cloth is properly maintained when it isdetermined that said predetermined number of workpieces has beenpolished; and dressing said polishing cloth by using a second dresserwhen it is determined that said polishing performance of said polishingcloth is not properly maintained.
 4. A method comprising: dressing apolishing cloth by using a first dresser; polishing a surface of aworkpiece by pressing said workpiece against said polishing cloth;determining whether or not a polishing performance of said polishingcloth is properly maintained; and dressing said polishing cloth by usinga second dresser when it is determined that said polishing performanceof said polishing cloth is not properly maintained, wherein said firstdresser has a diameter smaller than a diameter of said workpiece.
 5. Amethod comprising: dressing a polishing cloth by using a first dresser;polishing a surface of a workpiece by pressing said workpiece againstsaid polishing cloth; determining whether or not a polishing performanceof said polishing cloth is properly maintained; and dressing saidpolishing cloth by using a second dresser when it is determined thatsaid polishing performance of said polishing cloth is not properlymaintained, wherein said second dresser comprises a diamond dresser. 6.A method comprising: dressing a polishing cloth by using a firstdresser; polishing a surface of a workpiece by pressing said workpieceagainst said polishing cloth; determining whether or not a polishingperformance of said polishing cloth is properly maintained; and dressingsaid polishing cloth by using a second dresser when it is determinedthat said polishing performance of said polishing cloth is not properlymaintained, wherein said second dresser has a diameter larger than adiameter of said workpiece.
 7. A method comprising: dressing a polishingcloth under a first dressing condition; polishing a surface of aworkpiece by pressing said workpiece against said polishing cloth;measuring a profile of said surface of said workpiece; determiningwhether or not said profile of said surface of said workpiece meets apredetermined level requirement; and dressing said polishing cloth undera second dressing condition when it is determined that said profile ofsaid surface of said workpiece does not meet said predetermined levelrequirement.
 8. The method as recited in claim 7, further comprising:repeating dressing of said polishing cloth under said first dressingcondition and polishing of said surface of said workpiece by pressingsaid workpiece against said polishing cloth when it is determined thatsaid profile of said surface of said workpiece meets said predeterminedlevel requirement.
 9. The method as recited in claim 7, furthercomprising: repeating dressing of said polishing cloth under said firstdressing condition and polishing of said surface of said workpiece bypressing said workpiece against said polishing cloth; and determiningwhether or not a predetermined number of workpieces has been polished,wherein determining whether or not said profile of said surface of saidworkpiece meets a predetermined level requirement comprises determiningwhether or not said profile of said surface of said workpiece meets saidpredetermined level requirement when it is determined that saidpredetermined number of workpieces has been polished.
 10. A methodcomprising: dressing a polishing cloth under a first dressing condition:polishing a surface of a workpiece by pressing said workpiece againstsaid polishing cloth; measuring a profile of said surface of saidworkpiece; measuring a profile of said polishing cloth; determiningwhether or not said profile of said surface of said workpiece and saidprofile of said polishing cloth meet a predetermined level requirement;and dressing said polishing cloth under a second dressing condition whenit is determined that said profile of said surface of said workpiece andsaid profile of said polishing cloth do not meet said predeterminedlevel requirement.
 11. The method as recited in claim 10, furthercomprising: repeating dressing of said polishing cloth under said firstdressing condition and polishing of said surface of said workpiece bypressing said workpiece against said polishing cloth when it isdetermined that said profile of said surface of said workpiece and saidprofile of said polishing cloth meet said predetermined levelrequirement.
 12. The method as recited in claim 10, further comprising:repeating dressing of said polishing cloth under said first dressingcondition and polishing of said surface of said workpiece by pressingsaid workpiece against said polishing cloth; and determining whether ornot a predetermined number of workpieces has been polished, whereindetermining whether or not said profile of said surface of saidworkpiece and said profile of said polishing cloth meet saidpredetermined level requirement comprises determining whether or notsaid profile of said surface of said workpiece and said profile of saidpolishing cloth meet said predetermined level requirement when it isdetermined that said predetermined number of workpieces has beenpolished.